Figure 20: Initial Odyssian benchscale system
Odyssian’s bench scale microgrid is a single-phase system consisting of several 200W/240V microinverters that are connected through a single transformer to a collection of e-board load shedding devices. A simPower model for a simplified version of this testbed was built. The simplifications were needed to ensure that the simulation run time was not overly long. The modified testbed is shown in the block diagram (figure 20). This system consists of the main grid, a single inverter connected through a “smart” switch, and step-down transformer (240V to 120V) and two eboard modules. One e-board module has a critical load of 120 W and the other has a non-critical load of 60 W.
The single-phase inverter models the system as a voltage source with an LC filter. To preserve system stability the inductor in this filter had to be chosen rather large (1.e-1). Subsequent discussions with UIUC indicated that they were connecting their inverters as current sources, rather than voltage sources, to avoid such large components. A block diagram for the simPower voltage-source inverter is shown below.
Figure 21: Single phase inverter (simPower) model
The preceding system was simulated with the following events.
Time
seconds
|
Event
|
0.0
|
Simulation starts with main grid connected, e-boards disconnected, inverter disconnected (Preq= 0.8 pu)
|
0.1
|
e-board loads (180 W) connected.
|
2.0
|
Inverter (Preq=0.8 pu) connects.
|
3.0
|
Inverter setpoint reduced to Preq = 0.2 pu.
|
4.0
|
Microgrid islands.
|
4.3
|
e-board sheds non-critical (60W) load
|
6.0
|
Inverter setpoint increased to Preq = 0.8 pu.
|
7.1
|
e-board reconnects non-critical (60W) load.
| |
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